Osmosis is the movement of water molecules from a region of higher concentration to a region of lower concentration across a partially permeable membrane, so that eventually two solutions will have uniform water potential.
Osmosis is generally about:
A hypotonic solution has a higher water potential than a hypertonic solution.
In our experiment
The objective of our experiment was to prove that osmosis occurs as water molecules move from a hypotonic solution to a hypertonic solution.
The objective of our experiment was to prove that osmosis occurs as water molecules move from a hypotonic solution to a hypertonic solution.
Procedures
Step 1: Prepare a cylindrical gas jar with water. Add a few drops of iodine solution so that water turns a visible yellow.
Step 2: Tie one end of the Visking tubing tightly with thread. We need to ensure that there will not be leaks.
Step 3: Using a dropper, insert 3% starch solution to 3/4 of Visking tubing.
Step 4: Insert delivery tube into Visking tubing. We can’t have air bubbles getting into the delivery tube as this will affect the starch solution level in the delivery tube.
Step 5: Tie the other end of the Visking tubing tightly with thread.
Step 6: Using a dropper, add 3% starch solution into delivery tube to ensure that the starch solution level is clear the visible.
Step 7: Rinse the Visking tubing with water lightly to get rid of starch solution that could have accidentally gotten on the external surface of Visking tubing.
Step 8: Using a retort stand, suspend the delivery tube with attached Visking tubing into the gas jar as shown below.
This, however, is a failed experiment because the starch solution is leaking at a very fast rate as seen by the violet trails in the iodine solution. Presence of starch stains iodine violet.
This is how the set-up should look like:
Results
Explanation:The 3% starch solution in the visking tubing turned dark blue because of the iodine molecules which diffused from the solution in the glass jar into the visking tubing. The iodine molecules moved from a region of higher concentration (outside the visking tubing) to a region of lower concentration (in the visking tubing), thus showing it moved by diffusion.
We also observed that the level of starch solution in the glass tube rose slightly due to the movement of water molecules from the iodine solution into the 3% starch solution by osmosis. This is because water moved from a region of higher concentration of water molecules though the partially permeable membrane (the visking tubing) to a region of lower concentration of water molecules.
The starch molecules did not move out of the visking tubing because starch molecules are too big and cannot diffuse across the visking tubing. Thus, only the contents of the visking tubing turned dark blue because the iodine reacted with the starch.
By Gabriel Woon, Hilda Foo and Joey Lim
